Add I2CSlave to ov580 master.

Dependencies:   MorseGenerator2

Revision:
26:9ad740976a72
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed-os-retarget-segger-rtt.lib	Thu May 02 21:55:46 2019 +0000
@@ -0,0 +1,1 @@
+https://github.com/0x6d61726b/mbed-os-retarget-segger-rtt/#648b5440bd2744c5356c73b9bfdf8081ca65d79a